The present invention relates to drawing instruments and more particularly to a device and accessories thereto for facilitating the making of perspective drawings.
In perspective drawing, a plurality of straight line segments are drawn toward one or more vanishing points. A conventional method for drawing line segments toward a vanishing point is to locate a pin at the vanishing point and hold a ruler or guide against the pin while guiding a drawing device along the bar. A prior art improvement of this method is to provide a locating slot or hole in the bar for keeping the bar engaged with the pin.
In order to permit the vanishing point to be located between the reach of the bar, and to avoid a requirement for a long, clumsy guide bar, some drawing instruments of the prior art incorporate a mechanism for pivoting one or more bars about corresponding remotely located points as the bars are moved about on the drawing surface.
Many of the devices for producing perspective drawings in the prior art exhibit at least some of the following disadvantages:
1. They are ineffective in that they are limited to certain viewing angles and small drawing sizes; PA0 2. They are not portable in that they require a custom-built drawing table; PA0 3. They are inaccurate in that they do not maintain a selected vanishing point; PA0 4. They have limited use in that they are not suitable for drawing parallel lines; PA0 5. They are expensive to produce in that they incorporate elaborate mechanisms requiring tight manufacturing tolerances; PA0 6. They are hard to use in that they require a complicated mechanism adjustment; PA0 7. They are cumbersome in that they obstruct the drawing surface; and PA0 8. They are unwieldy in that they require rigid movable members extending to distant vanishing points. PA0 (a) locating first anchor means at the first vanishing point; PA0 (b) connecting a first flexible member at a first end thereof to the first anchor means; PA0 (c) connecting a second end of the first flexible member to a first tensioning spool, the first tensioning spool being mounted to a straightedge, the first flexible member forming a first ray portion radiating on a straight line from the first vanishing point, PA0 (d) positioning the straightedge on the drawing surface so that the first ray portion points along a selected one of the line elements; and PA0 (e) aligning the straightedge with the first ray portion of the first flexible member. PA0 (a) locating second anchor means at the second vanishing point; PA0 (b) connecting a second flexible member at a first end thereof to the second anchor means; PA0 (c) connecting a second end of the second flexible member to a second tensioning spool, the second tensioning spool being mounted to a straightedge, the second flexible member forming a second ray portion radiating on a straight line from the second vanishing point; PA0 (d) positioning the straightedge on the drawing surface so that the second ray portion points along a selected one of the line elements; and PA0 (e) aligning the straightedge with the second ray portion of the second flexible member.
Thus there is a need for perspective drawing instrument that is effective, portable, accurate, versatile, inexpensive to produce, and easy to use.